WASHINGTON — Americans for Prosperity unleashed two more rounds of ads Thursday attacking President Obama's health care law, bringing to $27 million the amount it has poured into an aggressive campaign to blister the law and Democrats who supported it ahead of the midterm elections.

The conservative advocacy group, aligned with billionaire industrialists David Koch and Charles Koch, plans to spend $400,000 on ads targeting Florida Democratic Reps. Alan Grayson and Joe Garcia. It also released a new online commercial today that seizes on a new federal report that concludes the law could reduce the number of full-time workers in the USA by more than 2 million. The Congressional Budget Office report says that would happen because people may choose to work fewer hours if they can do so without losing health insurance.

The grim ad accuses Obama of lying about the law's impact and says the reduction in full-time employment will hurt "the economy and middle-class families."

The advertising barrage from the group has rattled Democrats, who are fighting to retain their hold on the Senate majority in November. The group's biggest spending target — nearly $7.4 million to date — is North Carolina Sen. Kay Hagan, one of four incumbent Democratic senators seeking re-election in states won by Republican presidential candidate Mitt Romney in 2012.

Republicans need a net gain of six seats to capture the majority in the Senate.

"We intend to keep going," said Americans for Prosperity spokesman Levi Russell. "The bad news about Obamacare keeps rolling out, and we need to help people remember who voted for this law."

Driven largely by the group's spending, the advertising activity in House and Senate races "right now is more intense than it has ever been before," said Elizabeth Wilner, who tracks political commercials at Kantar's Campaign Media Analysis Group.

"These guys and others on the Republican side have demonstrated that they are going to go all out," said Tad Devine, a veteran Democratic strategist in Washington. While commercials broadcast in February might be forgotten by voters in November, the early barrage takes a toll because it "forces incumbents and strong challengers to spend money early, so they won't have it later," he said.

Sen. Mary Landrieu, D-La., the target of a steady stream of health-care-related ads from Americans for Prosperity, launched her first commercial of the campaign Dec. 11 — nearly a year ahead of Election Day.

New campaign finance reports show Democratic super PACs outraising Republican political committees. But Americans for Prosperity operates outside that system.

It is organized as a nonprofit social welfare organization and is supposed to avoid partisan politics. In its ads, it steers clear of calling for the election or defeat of candidates. Instead, it funds "issue ads," which criticize the health care law and urge voters to call individual lawmakers to sound off on the legislation. As a nonprofit, AFP does not have to disclose its donors.

Russell said the ads are not political, but part of a five-year strategy by the group to highlight the flaws of the law and work for its repeal. "Now that the bad news we've been worrying about is starting to affect people, we want politicians and policymakers to hear from that people that they don't like it," he said.

In the face of the unrelenting attacks, Democratic Party officials this week sought to link the GOP candidates benefiting from the outside spending with the policies of the Kochs and Americans for Prosperity.

Both Landrieu and her leading GOP rival, Rep. Bill Cassidy, back a delay in the big increases in the premiums homeowners will pay as part of the National Flood Insurance Program — a significant issue for voters in flood-prone parts of Louisiana. AFP has backed a measure that would allow the rate increases to take effect, but would phase them in slowly.

Justin Barasky, a spokesman for the Democratic Senatorial Campaign Committee, said AFP's heavy spending in key races "props up Senate candidates who will do their bidding" in Congress.

Cassidy spokesman John Cummins called it a "stretch" to link AFP's position on the flood-insurance program to Cassidy, who has aggressively sought to delay the premium hikes. "There's no coordination" between the Republican's campaign and the advocacy group, he said.

Russell said Democrats are "attacking the messenger rather than dealing with the policy issues they are responsible for."